Hi,
I just bought a xfx HD 7850 and I had all sort of problems with it.
I ran 3d mark and went from 2279 pts to 6698 witch was great !!!
But as soon as I got into games: green or gray screen with sound loop and hat to hard reset the computer
I tried to play planetside 2, payday, the godfather (old game ) all did the same thing.
Tried different resolution / setting : same thing.
I then tried different drivers (new one, the one on disk and beta)
On the beta one the dvi port on my screen broke (screen still work on vga but not dvi)
I might of been out of luck, but I am sticking to nvidia from now on.
I always run into trouble with ati/amd graphic cards.
My 2 cents